Bore wear compensating bit holder and bit holder block

ABSTRACT

A bit assembly includes a base block and a bit holder having a forward body portion and a shank. The bit holder includes a diametrically expanding retainer circumferentially disposed around a shank of the bit holder adapted to maintain the interference contact between the bit holder and the base block as the diameter of a bore of the base block increases from use. The bit assembly also includes a sealing gasket that forms a force fit between a washer disposed about the shank of the bit holder and the base block.

TECHNICAL FIELD

This disclosure relates to bit assemblies for road milling, mining, and trenching equipment.

BACKGROUND

Road milling, mining, and trenching equipment utilizes bits traditionally set in a bit assembly having a bit holder and a bit holder block. The bit is retained by the bit holder and the bit holder is retained within a bore in the bit holder block. A plurality of the bit assemblies are mounted on the outside of a rotatable drum, typically in a V-shaped or spiral configuration. The combinations of bit assemblies have been utilized to remove material from the terra firma, such as degrading the surface of the earth, minerals, cement, concrete, macadam or asphalt pavement. Individual bits, bit holders, and bit holder blocks may wear down or break over time due to the harsh road degrading environment. Additionally, the forces and vibrations exerted on the bit assemblies may cause the bit holder to wear away the bore of the bit holder block. As a result, the diameter of the bore of the bit holder block increases over time, decreasing the interference contact between the bit holder and the bore of the bit holder block, damaging the bit holder block, and requiring replacement of the bit holder block long before the standard minimum lifetime required by the industry. To prolong the life of the bit assembly, and the bit holder block, a bit holder comprising a diametrically expanding retainer circumferentially disposed around the shank of the bit holder is provided to maintain the interference contact between the bit holder and the bore of the bit holder block as the diameter of the bore of the bit holder block increases from use.

SUMMARY

This disclosure relates generally to bit assemblies for road milling, mining, and trenching equipment. One implementation of the teachings herein is a bit holder that includes a bit holder body, a shank axially depending from the bit holder body, a retainer disposed circumferentially about the shank, and a washer disposed circumferentially about the shank. The retainer further includes a slot axially extending along a length of the retainer.

These and other aspects of the present disclosure are disclosed in the following detailed description of the embodiments, the appended claims and the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The various features, advantages, and other uses of the apparatus will become more apparent by referring to the following detailed description and drawings, wherein like reference numerals refer to like parts throughout the several views. It is emphasized that, according to common practice, the various features of the drawings are not to-scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity.

FIG. 1 is a side plan view of a bit holder, showing Area A;

FIG. 2 is a detail side plan view of Area A of the bit holder of FIG. 1;

FIG. 3 is a side plan view of a bit assembly, showing Area B when the bit holder is initially inserted into a bit holder block;

FIG. 4 is a detail side plan view of Area B of the bit assembly of FIG. 3;

FIG. 5 is a side plan view of the bit holder, showing Area C;

FIG. 6 is a detail plan view of Area C of the bit holder of FIG. 5;

FIG. 7 is a side plan view of the bit assembly, showing Area D when the bit holder is completely inserted into the bit holder block;

FIG. 8 is a detail plan view of Area D of the bit assembly of FIG. 7;

FIG. 9 is a side plan view of the bit assembly, showing Area G when the bit holder is disposed within a new bit holder block;

FIG. 10 is a detail plan view of Area G of the bit assembly of FIG. 9;

FIG. 11 is a side plan view of the bit assembly, showing Area H when the bit holder block is worn approximately 0.005 inches;

FIG. 12 is a detail plan view of Area H of the bit assembly of FIG. 11;

FIG. 13 is a side plan view of the bit assembly, showing Area J when the bit holder block is worn approximately 0.010 inches;

FIG. 14 is a detail plan view of Area J of the bit assembly of FIG. 13;

FIG. 15 is a side elevation view of the bit assembly, showing Area M;

FIG. 16A is a detail cross-sectional view of Area M of the bit assembly of FIG. 15, showing an o-ring gasket;

FIG. 16B is a detail cross-sectional view of Area M of the bit assembly of FIG. 15, showing a quad-ring gasket;

FIG. 17 is an exploded side elevation view of the bit assembly of FIG. 15;

FIG. 18 is an exploded perspective view of the bit assembly of FIG. 15; and

FIG. 19 is a side elevation view of the bit assembly of FIG. 15.

DETAILED DESCRIPTION

Road milling, mining, and trenching equipment utilizes bits traditionally set in a bit assembly having a bit holder, comprising a bit holder body and a shank, and a bit holder block. The bit is retained by the bit holder and the shank of the bit holder is retained within a bore in the bit holder block. The combinations of bit assemblies have been utilized to remove material from the terra firma, such as degrading the surface of the earth, minerals, cement, concrete, macadam or asphalt pavement. Individual bits, bit holders, and bit holder blocks may wear down or break over time due to the harsh road degrading environment. Tungsten carbide and diamond or polycrystalline diamond coatings, which are much harder than steel, have been used to prolong the useful life of bits and bit holders. Bit holder blocks, herein after referred to as base blocks, are generally made of steel. Forces, vibrations, and loose abrasive materials exerted on the bit assemblies may cause the shank and the bit holder to wear away the bore of the base block. As a result, the diameter of the bore of the base block increases over time, decreasing, if not eliminating, the interference contact between the shank of the bit holder and the bore of the base block and damaging the base block. The damage to the base block may require replacement of the base block long before the standard minimum lifetime required by the industry. One important aspect of the present disclosure is to provide a bit holder, pick, or bit/holder combination, hereinafter referred to as bit holder, comprising a diametrically expanding retainer circumferentially disposed around the shank of the bit holder adapted to maintain the interference contact between the bit holder and the base block as the diameter of the bore of the base block increases from use, thereby prolonging the life of the base block and the bit assembly. Another important aspect of the present disclosure is to provide a sealing gasket between a washer disposed about the shank of the bit holder and the base block, providing an additional force fit between the bit holder and base block.

Referring to FIGS. 3, 7, 9, 11, 13, 17, and 18, an illustrated embodiment of a bit assembly 10 comprises a bit 12, bit holder 14, and a base block 16. The bit holder 14 includes a bit holder body 18 and a shank 20 axially depending from the bottom of the bit holder body 18. The bit holder body 18 is generally annular in shape and comprises a flat annular top surface 22 adjacent to an upper body portion 24 that includes an annular trough 26 in which to retain the bit 12. The upper body portion 24 generally slopes axially and radially outwardly to an arcuate first mediate portion 28. The first mediate portion 28 generally slopes axially and radially outwardly to a second mediate portion 30. The second mediate portion 30 generally slopes axially and radially outwardly to a radially extending generally arcuate tire portion 32. A decreased diameter tapered distal portion 36 extends from a flange 34, such as a flat annular flange, subjacent to the tire portion 32.

The shank 20, shown in FIGS. 1, 3, 5, 7, 9, 11, 13, 17, and 18, axially depends from the decreased diameter tapered distal portion 36 of the bit holder body 18. The bit holder body 18 and the shank 20 are axially aligned about a bit holder bore 56 (not shown) that extends from the flat annular top surface 22 of the bit holder body 18 to a distal end 44 of the shank 20. The shank 20 comprises a generally cylindrical decreased diameter upper segment 38 that axially extends from the decreased diameter tapered distal portion 36 and a generally cylindrical increased diameter lower segment 40. Subjacent the lower segment 40 is a decreased diameter distal segment 42 that axially extends from the lower segment 40 to the distal end 44 of the shank 20. In other embodiments, the shank 20 can be cylindrical or can include tapered and arcuate segments.

The shank 20 includes a coaxial and generally cylindrical collapsible retainer 46, shown in FIGS. 1-14 and 16-18, that is disposed circumferentially about the shank 20. The retainer 46 is generally made from spring steel or other hardenable material with an elasticity that allows the retainer 46 to return to its original shape despite significant deflection or twisting. The axial length of the retainer 46 is shorter than the axial length of the shank 20 between point “A” and point “B,” as shown in FIG. 1. In the embodiment of FIG. 1, the typical difference 74 between the retainer 46 length and the shank 20 axial length between point “A” and point “B” is in the range of approximately 0.040 to 0.060 inches, however, the typical difference 74 between point “A” and point “B” may be varied depending on the applicable circumstances. The retainer 46 includes a slot 48 that axially extends along the length of the retainer 46. A washer 50 is disposed circumferentially about the retainer 46 and the shank 20. The washer 50 includes a first inner portion 52 and a second inner portion 54, shown in FIGS. 2, 4, 6, 8, 10, 12, 14, and 18, where the first inner portion 52 is adjacent the second inner portion 54. The first inner portion 52 is tapered to comprise the same dimensions as the dimensions of the decreased diameter tapered distal portion 36. The second inner portion 54 comprises a reverse taper such that the angle of the reverse taper is adapted to urge the washer 50 forward when an interference contact is formed between the retainer 46 and the base block 16. In an alternate embodiment, the washer 50 includes an annular sealing gasket 60, shown in FIGS. 17 and 18, disposed in a groove 51, shown in FIGS. 16A and 16B, on a rear face 72 of the washer 50 that is adapted to contact and form a seal with a forward face 70 of the base block 16, thereby providing a force fit between the washer 50 and the base block 16. The sealing gasket 60 can be an o-ring gasket 76, shown in FIG. 16A, a quad-ring gasket 78, shown in FIG. 16B, or similar sealing gasket, gasket seal, or gasket forming a seal.

The base block 16, shown in FIGS. 3, 7, 9, 11, 13, 15, and 17-19, comprises a base 62 and a front end 64. The base 62 can be flat or slightly concave to fit a drum or additional mounting plates on which a plurality of base blocks can be mounted. The front end 64 includes a base block bore 58, shown in FIG. 18, that is symmetrical with the shank 20 along a centerline. The base block bore 58 can be machined in a precision manner or other similar manner.

When assembled, slot 48 allows the retainer 46 to radially compress when inserted into the base block bore 58 of the front end 64, forming an interference contact between the retainer 46, the shank 20, and the base block bore 58. The force between the diametrically contracted retainer 46 and the base block bore 58 maintains and retains the bit holder 14 in the base block 16. The bit holder 14 and the base block 16 are assembled together to form the bit assembly 10. When assembled, the sealing gasket 60 forms a seal between the washer 50 and the front end 64 of the base block 16, as shown in Detail H of FIGS. 16A and 16B. The bit holder body 18, shank 20, bit holder bore 56 of bit holder 14, front end 64, and base block bore 58 of base block 16 are axially aligned when assembled together to form the bit assembly 10. The diameter of the retainer 46 matches the inner diameter of the base block bore 58 until the base block 16 needs to be replaced.

Over time, the forces, vibrations, and loose abrasive materials exerted on the bit assembly 10 through road milling, mining, and trenching operations wear away at the bit 12 and the base block bore 58, increasing the diameter of the base block bore 58. Bits 12 are typically replaced every 1-2 days. Each time a new bit 12 is driven into the bit holder 14, the washer 50 is driven into the forward face 70 of the base block 16. Since the length of the retainer 46 is less than the length of the shank 20 between point “A” and point “B,” there will be some axial movement of the retainer 46 based on the angle of the second inner portion 54 of the washer 50.

To prolong the life of the base block 16, the retainer 46 is expanded to match the diameter 68 of the base block bore 58. As the diameter 68, shown in FIG. 8, of the base block bore 58 increases due to bore wear, the retainer 46 moves diametrically towards the washer 50 where the contact at point “C” of the second inner portion 54 urges the retainer 46 to move toward point “A,” shown in FIG. 1, thereby reducing the space between the contact at point “C” and point “A” and increasing the diameter of the retainer 46 to match the diameter 68 of the base block bore 58. When the diameter of the retainer 46 matches the diameter 68 of the base block bore 58, an interference contact is again formed between the retainer 46 and the base block bore 58, and the washer 50 is in turn urged forward towards the bit holder body 18. As the retainer 46 is further expanded and the washer 50 is further urged forward, the contact at point “C” is moved towards the rear face 72 of the washer 50, as shown sequentially in FIGS. 10, 12, and 14. As the angle of the reverse taper of the second inner portion 54 is decreased or increased, an increase or decrease, respectively, also occurs with the axial movement of the washer 50. Eventually, all space between point “A” and point “E” will be eliminated, thereby eliminating the distance between a forward face 66 of the washer 50 and the flange 34 of the bit holder body 18.

For illustration purposes, the bit assembly 10 is shown at three stages of the life time of the base block 16. FIGS. 9 and 10 show a new base block 16 in bit assembly 10. In the illustrated embodiment, when the base block 16 is new, the diameter 68 of the base block bore 58 is a nominal 0.880 inches, however, the diameter 68 may be varied depending on the applicable circumstances. In this illustrated embodiment, the initial diameter of the retainer 46 is in the range of approximately 0.935-0.960 inches, however, the diameter of the retainer 46 may also be varied depending of the applicable circumstances. The diameter of the retainer 46 is then pre-compressed to a diameter smaller than the diameter 68 of the base block bore 58 to allow manual pre-insertion of the shank 20 into the base block bore 58. The diameter of the retainer 46 is thereby collapsed to 0.880 inches to match the diameter 68 of the base block bore 58 when the bit holder 14 is initially installed in the base block 16. The gap between the forward face 66 of the washer 50 and the flange 34 of the bit holder body 18 is approximately 0.042 inches, as shown by Detail G in FIG. 10, when the base block 16 is new.

In the illustrated embodiment, FIGS. 11 and 12 show the base block 16 in bit assembly 10 when the base block bore 58 is worn approximately 0.005 inches. When the base block bore 58 is worn approximately 0.005 inches, the diameter 68 of the base block bore 58 is approximately 0.885 inches. The forces and vibrations exerted on the bit assembly 10 when it is in use will move the retainer 46 towards the washer 50 as the diameter 68 of the bore 58 increases. The retainer 46 will then make contact with a new point “C,” shown in FIG. 12, which will force the retainer 46 to expand radially. The diameter of the retainer 46 is then expanded to 0.885 inches to match the diameter 68 of the base block bore 58, forming an interference contact between the retainer 46 and the base block bore 58. Once the interference contact is formed, the retainer 46 and base block 16 will force the washer 50 to move towards the bit holder body 18, decreasing the gap between the forward face 66 of the washer 50 and the flange 34 of the bit holder 14. The gap between the forward face 66 of the washer 50 and the flange 34 of the bit holder body 18 is then reduced to approximately 0.027 inches, as shown by Detail H in FIG. 12, when the base block bore 58 is worn approximately 0.005 inches.

In the illustrated embodiment, FIGS. 13 and 14 show the base block 16 in bit assembly 10 when the base block bore 58 is worn approximately 0.010 inches. When the base block bore 58 is worn approximately 0.010 inches, the diameter 68 of the base block bore 58 is approximately 0.890 inches. The forces and vibrations exerted on the bit assembly 10 when it is in use will move the retainer 46 towards the washer 50 as the diameter 68 of the bore 58 increases. The retainer 46 will then make contact with a new point “C,” shown in FIG. 14, which will force the retainer 46 to expand radially. The diameter of the retainer 46 is then expanded to 0.890 inches to match the diameter 68 of the base block bore 58 forming an interference contact between the retainer 46 and the base block bore 58. Once the interference contact is formed, the retainer 46 and base block 16 will force the washer 50 to move towards the bit holder body 18, decreasing the gap between the forward face 66 of the washer 50 and the flange 34 of the bit holder 14. The gap between the forward face 66 of the washer 50 and the flange 34 of the bit holder body 18 is then reduced to approximately 0.013 inches, as shown by Detail J in FIG. 14, when the base block bore 58 is worn approximately 0.010 inches.

As the diameter 68 of the base block bore 58 increases, the retainer 46 is expanded and the diameter of the retainer 46 increases to reform an interference contact between the retainer 46 and the base block 16. The process continues until the gap between the forward face 66 of the washer 50 is eliminated and varies depending on the size of the shank 20. When the base block bore 58 is worn beyond this point, and the diameter of the retainer 46 can no longer expand, the base block 16 must be replaced.

While the present disclosure has been described in connection with certain embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is permitted under the law. 

1. A bit holder comprising: a bit holder body; a shank axially depending from the bit holder body; a retainer disposed circumferentially about the shank, the retainer comprising a slot axially extending along a length of the retainer; and a washer disposed circumferentially about the shank.
 2. The bit holder of claim 1, further comprising: a sealing gasket disposed circumferentially about the shank, the sealing gasket adapted to form a seal between the washer and the bit holder block.
 3. The bit holder of claim 2, wherein the sealing gasket is one of an o-ring or a quad-ring.
 4. The bit holder of claim 1, further comprising: an annular groove on a rear face of the washer; and a sealing gasket disposed in the annular groove, the sealing gasket adapted to form a seal between the washer and the bit holder block.
 5. The bit holder of claim 4, wherein the sealing gasket is one of an o-ring or a quad-ring.
 6. The bit holder of claim 1, wherein an aperture of the washer includes a first tapered portion adjacent a second tapered portion.
 7. The bit holder of claim 6, wherein an angle of the second tapered portion is adapted to collapse the retainer and move the washer towards the bit holder body.
 8. The bit holder of claim 1, wherein the shank comprises an upper segment and a lower segment, and wherein a first axial length of the retainer is shorter than a second axial length of the upper segment.
 9. The bit holder of claim 1, wherein a diameter of the retainer is initially at least 0.935 inches.
 10. A combination bit holder and base block comprising: the bit holder comprising: a bit holder body; a shank axially depending from the bit holder body; a retainer disposed circumferentially about the shank, the retainer comprising a slot axially extending along a length of the retainer; and a washer disposed circumferentially about the shank; and the base block comprising a bore adapted to make an interference contact with the retainer of the bit holder.
 11. The combination bit holder and base block of claim 10, further comprising: a sealing gasket disposed circumferentially about the shank, the sealing gasket adapted to form a seal between the washer and the base block.
 12. The combination bit holder and base block of claim 11, wherein the sealing gasket is one of an o-ring or a quad-ring.
 13. The combination bit holder and base block of claim 10, wherein the washer is adapted to axially collapse the retainer.
 14. The combination bit holder and base block of claim 10, further comprising: an annular groove on a rear face of the washer; and a sealing gasket disposed in the annular groove, the sealing gasket adapted to form a seal between the washer and the base block.
 15. The combination bit holder and base block of claim 14, wherein the sealing gasket is one of an o-ring or a quad-ring.
 16. The combination bit holder and base block of claim 10, wherein an aperture of the washer includes a first tapered portion adjacent a second tapered portion.
 17. The combination bit holder and base block of claim 16, wherein an angle of the second tapered portion is adapted to collapse the retainer and move the washer towards the bit holder body.
 18. The combination bit holder and base block of claim 10, wherein a diameter of the retainer is adapted to expand to an inner diameter of the bore to form the interference contact between the retainer and the bore of the base block.
 19. The combination bit holder and base block of claim 18, wherein a distance between the washer and an annular flange of the bit holder body is adapted to decrease as the diameter of the retainer increases.
 20. The combination bit holder and base block of claim 10, wherein the shank comprises an upper segment and a lower segment, and wherein a first axial length of the retainer is shorter than a second axial length of the upper segment.
 21. The combination bit holder and base block of claim 10, wherein a diameter of the retainer is initially at least 0.935 inches.
 22. The combination bit holder and base block of claim 10, wherein an inner diameter of the bore of the base block is a nominal 0.880 inches.
 23. The combination bit holder and base block of claim 16, wherein the enlargement of the base block bore allows the retainer outer diameter to enlarge and a leading tapered surface of the retainer impinging on the second tapered surface of the washer moves the washer towards the bit holder body. 